Structure-chiroptical properties relationship of carbapenams by experiment and theory

The present work examines the relationship between the molecular structure and chiroptical properties of carbapenams through use of electronic circular dichroism spectroscopy (ECD). The applicability of the helicity rule that correlates the molecular structures of various β-lactam analogues and their ECD spectra is examined against a set of differently substituted carbapenams. It is demonstrated that the studied compounds conform to the rule. The rule can be also applied to the carbapenams with an additional chromophoric unit interfering with the amide chromophore. For the representative carbapenams, the experimental curves are compared to the ECD spectra computed using time-dependent density functional theory (TDDFT) in order to validate the experimental data. The study reveals a high effectiveness of the ECD spectroscopy for the configurational assignment at the bridgehead carbon atom and demonstrates a strong dependence of the molecular conformation on substitution of the five-membered ring and side-chain flexibility of investigated carbapenams.